Damage Mechanics Model Of Rock Around Borehole Of Hydraulic Fracturing Well

The stress distribution status of rock around borehole of hydraulic fracturing are analyzed and calculated accurately, which provide a reliably theoretical basis for the research on initial fracturing and propagation law of fracture of hydraculic fractruing. The research of rock around borehole stress of hydraulic fracturing before were based on assumption that the surrounding rock medium of wellhole was completely elastomer without damage, then stress status around wellbore were analyzed. In fact, varying degree of damage about rock around borehole are get by bearing initial ground stress through the drilling and producing, at the same time, elastic area and damage area are existed. Due to the pressure of fracturing fluid in fractruing, the damge of rock around borehole is carring on and stress distribution status are changed. So, the former theory is not good enough for the research of stress distribution of rock around borehole.In this paper, rock around borehole before hydraulic fracturing is divided into damage area and the elastic area, and the size of damage area is calculated by yield surface equation, and considering infiltrating fluid action of the matrix pores fluid medium, a stress calculation model of damage area and elastic area of rock around borehole based on damage theory is established. Considering that damage of rock around borehole come from the fracturing fluid and alteration of stress status of rock around borehole in the fracture process, when we research the stress of rock around borehole of hydraulic fracturing, the surrounding rock of wellface are divied into failure area, damage area and elastic area, and a stress calculation of wellface surrounding rock which considered damage characteristics is built.Therefore, according to the research of stress distribution of rock around borehole that based on damage theory, the calculation of the stress distribution of rock around borehole of hydraulic fracturing is more exactly, which provide a reasonably theoretical basis for the improvement design of hydraulic fracturing and has an important academic value and practical significance.